Here is an exhaustive source of devious and magical things to do with Slush Powder. Wonderfully illustrated with that "cartoon" feel, it includes:

Instant Ventriloquist
Gelled Card The Hard Way
Tailgate Party
Burrrr
Four!
Cup Penetration
Slush-A-Cola
Slush In the News
Potty Humor
Have A Ball
Ultimate Slush Prank
Over Their Head
And much more! 18 tips and tricks in all.